1. Field of the Invention
The invention relates to a thread-tensioning device for being attached to a bobbin housing, the bobbin housing having a cylindrical jacket for surrounding a bottom-thread bobbin received therein.
2. Description of Related Art
Thread-tensioning devices mounted on bobbin-receiving housings are known. In one such device, a leaf spring is so fastened to the bobbin housing that its resilient end rests against a part of the bobbin housing whereby a clamping action is produced. The pressing force of the leaf spring is adjustable by a regulating screw therein. The bottom thread drawn off from a bottom-thread bobbin contained within the bobbin housing is conducted through the clamping location so that during the process of drawing off the thread a resultant thread-tensioning force made up of these components' braking force and detaining force is imposed upon it.
These known thread-tensioning devices have the disadvantage - since no sensing of the diameter of the package of thread is provided - that is present in all lock-stitch loopers known up to the present time, namely that the thread-tensioning force exerted upon the bottom thread when it is drawn off is less when the thread package is at its maximum diameter than when it is at its minimum diameter.